180 BIOGRAPHIES OF SCIENTIFIC MEN 



now they are utilized according to Gay-Lussac's method. 

 This consists in absorbing the vapours by means of 

 sulphuric acid of a specific gravity 176. On treating 

 this nitrous sulphuric acid with steam, nitrous fumes are 

 evolved and passed again into the chamber, while the 

 diluted sulphuric acid is again concentrated. 



In 1808 Gay-Lussac and Thenard prepared boron by 

 decomposing boron trioxide with potassium. They also 

 prepared boron fluoride by heating together boron trioxide 

 and calcium fluoride ; and they determined the composition 

 of boric acid both synthetically and analytically. In 

 1809 Gay-Lussac discovered the chemical action of light 

 on a mixture of hydrogen and chlorine; and in 1810, he 

 and The'nard examined hydrofluoric acid, which had been 

 discovered by Scheele in 1772. In the same year (1810) 

 they established the elementary nature of phosphorus, an 

 important investigation which led to the discovery of the 

 element's various allotropes. 



In 1814, the year that Napoleon defeated the Prussians 

 and signed his abdication of the throne of France, Gay- 

 Lussac and Davy discovered hydriodic acid, and examined 

 the element iodine which had been previously isolated by 

 Courtois (1811). Gay-Lussac also examined bromine, and 

 demonstrated the compound nature of fluor spar. 



In 1815 Gay-Lussac made a most important discovery, 

 namely, that of cyanogen gas ; and proved that this gas 

 habitually imitated the element chlorine in its com- 



